1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive film device, more particularly to a piezoelectric/electrostrictive film device including a structure in which a flexural displacement not less than that of a related-art device is secured, whereas a resonance frequency is high.
2. Description of the Related Art
In recent years, a piezoelectric/electrostrictive film device has been used in various applications such as a displacement control device, solid device motor, ink jet head, relay, switch, shutter, pump, optical modulation device, and fin. The piezoelectric/electrostrictive film device can control a minute displacement, and additionally has superior properties such as high electromechanical transduction efficiency, high-speed response, high durability, and low power consumption. In recent years, in the application of the ink jet head, there has been a demand for a device whose high-speed response is possible in order to enhance printing quality and speed.
Additionally, in general, the piezoelectric/electrostrictive film device includes a structure in which a lower electrode, piezoelectric/electrostrictive layer, and upper electrode are stacked in order on a substrate formed of ceramic. However, in order to secure insulation between the electrodes and avoid dielectric breakdown, as shown in FIG. 19, a piezoelectric/electrostrictive film device 30 has been developed in which an upper surface of a lower electrode 77 is coated with a piezoelectric/electrostrictive layer 73 and an end of the layer projects onto a substrate 44 (See JP-A-6260694).
Moreover, a projecting portion 79 of the piezoelectric/electrostrictive layer can directly be bonded to the substrate 44 formed of alumina. In this structure, since the opposite ends of the piezoelectric/electrostrictive layer 73 are fixed to inhibit the layer from contracting/expanding (the piezoelectric/electrostrictive layer contracts/expands in a vertical direction with respect to a thickness direction by applying a voltage), there is a problem that the flexural displacement is reduced. To solve the problem, in the related-art piezoelectric/electrostrictive film device 30, the projecting portion 79 of the piezoelectric/electrostrictive layer 73 has heretofore been disposed with respect to the substrate 44 in an incompletely coupled state (See JP-A-6-260694).
It is further disclosed that in the related-art piezoelectric/electrostrictive film device 30, to prevent disconnection of an upper electrode 75 by presence of a non-continuous surface generated between the projecting portion 79 of the piezoelectric/electrostrictive layer 73 disposed in the incompletely coupled state, and the substrate 44, a predetermined resin layer is formed between the projecting portion 79 of the piezoelectric/electrostrictive layer 73 and the substrate 44 (See JP-A-6-260694).
However, it has been recognized that in the related-art piezoelectric/electrostrictive device, the flexural displacement or a generative force is adversely influenced by the connection of the projecting portion of the piezoelectric/electrostrictive layer to the substrate. Based on this recognition, enlargement of rigidity of the device has not been considered at all. Therefore, the device cannot necessarily sufficiently meet the demand for the high-speed response in recent years.
That is, in the related-art piezoelectric/electrostrictive devices, almost all the resin layers have a remarkably low hardness as compared with a ceramic or metal material constituting the piezoelectric/electrostrictive layer, and the devices do not substantially contribute to enhancement of the rigidity of the device. In recent years, there has been a demand for a device which has the flexural displacement not less than that of the related-art and also has a high resonance frequency and in which a higher-speed response is possible. This demand has not necessarily sufficiently been satisfied.
Moreover, the resin layer is usually formed by coating a desired portion with a solution containing a resin component and solvent and thereafter drying the solution. However, in a drying step, the resin layer has large shrinkage, and there is a problem that cracks are easily generated in the resin layer, and in the piezoelectric/electrostrictive layer in some cases.
Furthermore, the piezoelectric/electrostrictive film device is requested to be repeatedly driven at a high speed, but the resin layer has a relatively small tenacity, and does not have sufficient resistance to the repeated high-speed driving. Therefore, the obtained piezoelectric/electrostrictive film device has not been necessarily sufficient in durability.